Login to the Mediavine Marketplace (please note that this is a specific login, separate from your Mediavine Dashboard login if you are a Mediavine publisher)
Hover over "Account", then select "Downloads":
3. Once you're on the Downloads page, it will look something like this, showing you all of your purchases with available downloads:
Then, just click on the link for the file you need in the right hand column, and a zip file will download to your device, which can then be uploaded to your Wordpress admin.